These observations suggest that a number of signals, delivered either by contact with stromal cells or by cytokines, prevent the apoptosis of CD10-positive ALL cells in vivo and facilitate their proliferation (Welch et al, 1990; Manabe et al, 1992, 1994; Saeland et al, 1992; Campana et al, 1994; Murti et al, 1996; Nishigaki et al, 1997). This evidence concerns the gene MME and acute lymphoblastic leukemia.